The present invention is related to electronic signal conversion, and more particularly to analog to digital converters.
A typical flash analog to digital converter circuit includes a resistor ladder used to generate a number of reference voltages for comparison with an input conversion voltage. Turning to FIG. 1, an exemplary prior art analog to digital converter circuit 100 including a resistor ladder is shown. Analog to digital converter circuit 100 includes a number of comparators 110. A negative input of each of the comparators is fed by the output of a respective multiplexer 120. Each of the multiplexers 120 selects between six different reference voltages generated by the resistor ladder. While three comparators 110, three multiplexers 120 and a resistor ladder including ten resistors are shown, more than these numbers may be included in the circuit as indicated by marks 195, 196.
As shown, the resistor ladder includes a number of resistors 160, 161, 162, 163, 164, 165, 166, 167, 168, 169 that are connected in series between a lower voltage potential 150 and an upper voltage potential 140. Each of the aforementioned resistors generates a distinct reference voltage that may be chosen for comparison by one of comparators 110. In particular, multiplexer 120a receives upper voltage potential 140, a voltage 170 that is one IR drop below upper voltage reference 140, a voltage 171 that is two IR drops below upper voltage reference 140, a voltage 172 that is three IR drops below upper voltage reference 140, a voltage 173 that is four IR drops below upper voltage reference 140, and a voltage 174 that is five IR drops below upper voltage reference 140. Multiplexer 120a is operable to select one of the aforementioned voltages to pass to comparator 110a for comparison with an input conversion voltage 190.
Multiplexer 120b receives voltage 172, voltage 173, voltage 174, a voltage 175 that is six IR drops below upper voltage reference 140, a voltage 176 that is seven IR drops below upper voltage reference 140, and a voltage 177 that is eight IR drops below upper voltage reference 140. Multiplexer 120b is operable to select one of the aforementioned voltages to pass to comparator 110b for comparison with input conversion voltage 190. Multiplexer 120c receives a number of voltages including lower voltage potential 150, a voltage 179 that is one IR drop above lower voltage potential 150, and a voltage 178 that is two IR drops above lower voltage potential 150. Multiplexer 120c is operable to select one of the aforementioned voltages to pass to comparator 110c for comparison with input conversion voltage 190.
Use of such a resistor ladder to provide the multiplicity of voltage references allows for reasonable calibration and operation of a flash analog to digital converter. However, implementing the resistor ladder requires considerable die area, and operation of the resistor ladder results in considerable power dissipation. Hence, for at least the aforementioned reasons, there exists a need in the art for advanced systems, circuits and methods for electronic signal conversion.